Cumyl alcohol is converted into cumene through hydrogenolysis in the presence of a copper-based catalyst. Herein, the copper-based catalyst is usually provided as a precursor in which copper contained therein is in an oxidized state, therefore, it requires a reduction by hydrogen in use. However, there is a problem that the reduction generates heat, the heat is accumulated in the catalyst thereby to cause sintering thereof and the like, and the catalyst is deteriorated. For avoiding the problem, there is a method of diluting hydrogen with a large amount of nitrogen to proceed the reduction mildly. However, there is a problem that this method requires a large amount of nitrogen, therefore, is not economical.